The present invention relates to a metal interconnection structure for evaluation on electromigration appeared therein, and more particularly to a metal interconnection structure for evaluation on reliability of a semiconductor device.
The electromigration has been known to be a phenomenon that metal ions in the metal interconnection in the semiconductor device are moved by exchange in momentum between electrons as current carriers flowing through the metal interconnection and the metal ions in the metal interconnection under an increased current density of the metal interconnection and/or an increased device temperature due to an increased power for each chip. The electromigration may cause a local formation of voids in the metal interconnection, whereby a resistance of the metal interconnection is increased and a disconnection to the metal interconnection appears. Namely, the electromigration deteriorates the reliability of the semiconductor device. For those reasons, it is important to do an evaluation on the electromigration of the metal interconnection of the semiconductor device.
FIG. 1 is a fragmentary plane view illustrative of a metal interconnection and a plug interconnection for connection to an electrode pad to conduct an electromigration-evaluation test. A plug interconnection 22 made of aluminum has a width wider than a metal interconnection 21 made of aluminum as a sample for evaluation on electromigration. The test is made by applying a current through the plug interconnection 22 and the metal interconnection 21, whereby electrons 25 move in a direction from the plug interconnection 22 to the metal interconnection 21, and also aluminum atoms 26 are moved by exchange in momentum with the electrons 25. Namely, the aluminum atoms 26 flow from the plug interconnection 22 to the metal interconnection 21. As described above, the plug interconnection 22 is wider than the metal interconnection 21. The plug interconnection 22 serves as a large aluminum atom donor which supplies aluminum atoms 26 to the metal interconnection 21. Supply of aluminum atoms 26 from the plug interconnection 22 to the metal interconnection 21 compensates electromigration of the metal interconnection 21, thereby disturbing the evaluation on electromigration.
In order to suppress that the aluminum atoms 26 in the plug interconnection 22 are moved into the metal interconnection 21, it was proposed that opposite ends of the metal interconnection 21 are terminated with other metal than aluminum. FIG. 2A is a fragmentary plane view illustrative of another connection structure of plug vias between an aluminum interconnection for evaluation on electromigration and an aluminum plug interconnection. FIG. 2B is a fragmentary cross sectional elevation view illustrative of the other connection structure of plug vias between an aluminum interconnection for evaluation on electromigration and an aluminum plug interconnection as shown in FIG. 2A. An aluminum interconnection 21 for evaluation on electromigration is connected through tungsten plug vias 24 to an aluminum plug interconnection 22. A current is applied from the aluminum plug interconnection 22 to the aluminum interconnection 21. The current causes aluminum atoms in the aluminum plug interconnection 22 to move toward one end thereof which is connected through the tungsten plug vias 24 to the aluminum interconnection 21. The aluminum atoms do not move through the tungsten plug vias 24 to the aluminum interconnection 21. The current flows from the aluminum plug interconnection 22 through the tungsten plug vias 24 to the aluminum interconnection 21. Aluminum atoms 26 in the aluminum interconnection 21 are moved by the electromigration without any supply of aluminum atoms from the aluminum plug interconnection 22. A discontinuation in flow of aluminum atoms causes the electromigration in the boundary between the aluminum interconnection and the tungsten plug vias. This electromigration forms voids. The movement of aluminum atoms by the electromigration is due to a drift of aluminum atoms in the aluminum interconnection.
The first test pattern shown in FIG. 1 has the following problems. The aluminum interconnection 21 to be evaluated on electromigration is connected with the wide aluminum plug interconnection 22 which is connected with the electrode pad not illustrated. Crystal grains 23 exist in not only the aluminum interconnection 21 but also the aluminum plug interconnection 22. Namely, aluminum atoms are likely to move along the crystal grains 23 not only in the aluminum interconnection 21 but also in the aluminum plug interconnection 22. The aluminum atoms flow from the aluminum plug interconnection 22 into the aluminum interconnection 21. This means that the aluminum atoms are supplied from the aluminum plug interconnection 22 into the aluminum interconnection 21, whereby even aluminum atoms in the aluminum interconnection 21 are moved by the electromigration, the supply of the aluminum atoms from the aluminum plug interconnection 22 compensate the electromigration in the aluminum interconnection 21, whereby an electromigration life-time is made long. Particularly, if the aluminum interconnection is abutted with a titanium layer, a TiAl alloy exists in the boundary between the aluminum interconnection and the titanium layer. Aluminum atoms are easy to move through a Tixe2x80x94Al interface. Namely, the aluminum atoms are easily to be supplied into the aluminum interconnection to be evaluated on electromigration. As a result, even the electromigration appears in the aluminum interconnection, externally supplied aluminum atoms may compensate the electromigration to suppress formation of voids in the aluminum interconnection. Further external supply of aluminum atoms into the aluminum interconnection to be evaluated on electromigration results in increase in volume of the aluminum interconnection and in reduction in resistance of the aluminum interconnection.
The second test pattern shown in FIG. 2 has a similar structure to the actual interconnection layout pattern, whereby an accurate evaluation on electromigration life-time of the aluminum interconnection. The second test pattern shown in FIG. 2 is, however, disadvantage in a complicated structure which needs a longer time necessary for forming the test pattern than the first test pattern of FIG. 1. As illustrated in FIG. 2B, the aluminum interconnection 21 to be evaluated on electromigration is formed at a different level from the aluminum plug interconnection 22. Further, the aluminum interconnection 21 and the aluminum plug interconnection 22 are connected to each other through the tungsten plug vias 24. FIG. 3 is a diagram illustrative of variations in resistance of the metal interconnections of the first and second test patterns shown in FIGS. 1 and 2A-2B versus time of electromigration test. The first test pattern remains in resistance due to supply of aluminum atoms from the aluminum plug interconnection and then decreases in resistance due to excess supply of aluminum atoms from the aluminum plug interconnection. Namely, the electromigration appeared in the aluminum interconnection is compensated by the supply of aluminum atoms from the aluminum plug interconnection. The wide aluminum interconnection has a large number of crystal grains which make it easy for aluminum atoms to move through the aluminum interconnection. Aluminum atoms are moved toward an anode whilst voids are moved toward a cathode. The voids are, however, filled up with the aluminum atoms supplied from the aluminum plug interconnection. The second test pattern remains in resistance before the electromigration appears but after the electromigration appears, the resistance increases apparently.
In order to prevent compensation to electromigration by external supply of aluminum atoms, the aluminum interconnection to be evaluated on electromigration is terminated with a different metal from aluminum. The multilevel interconnection structure is disadvantageous in many necessary fabrication steps with long times.
In order to solve the above problems and disadvantages, a different structure for evaluation on electromigration of the aluminum interconnection. FIG. 4 is a plane view illustrative of another conventional structure for evaluation on electromigration of the aluminum interconnection. An aluminum interconnection 21A to be evaluated on electromigration is terminated with two pads 22A, each of which has grid lines which are narrower than the aluminum interconnection 21A. This conventional technique is disclosed in Japanese Patent No. 2666774. Since the pads 22A have grid lines narrower than the aluminum interconnection 21A, electromigration is likely to appear in the wide aluminum interconnection 21A rather than the grid lines of the pads 22A. The pad 22A is longer in life-time than the aluminum interconnection 21A. It is rare that electromigration appears on the grid lines of the pads 22A and voids are formed in the grid lines of the pads 22A. Namely, there is almost no influence to the evaluation on electromigration of the aluminum interconnection 21A. Namely, an accurate evaluation on electromigration of the aluminum interconnection 21A is possible. It is, however, not easy to form the grid lines of the pads 22A. It is somewhat difficult to form the grid lines which are much narrower than the aluminum interconnection 21A. If the grid lines are not so narrower than the aluminum interconnection 21A, then it is possible that the pads 22A having such the grid lines reaches the end of its life-time prior to the aluminum interconnection 21A, whereby the evaluation on electromigration of the aluminum interconnection 21A is no longer possible. In the above Japanese patent publication, the interconnection to be evaluated on electromigration has a bamboo-structure, whereby the interconnection comprises a plurality of narrower parallel lines isolated from each other. The bamboo-structure makes the life-time longer than the pads on opposite ends of the bamboo-structured interconnection, whereby the pads reach the end of these life-time prior to appearance of electromigration in the bamboo-structured interconnection.
In the above circumstances, it had been required to develop a novel free from the above problem.
Accordingly, it is an object of the present invention to provide a novel metal interconnection structure for evaluation on electromigration free from the above problems.
It is a further object of the present invention to provide a novel metal interconnection structure for accurate evaluation on electromigration.
It is a still further object of the present invention to provide a novel metal interconnection structure for accurate evaluation on electromigration, wherein the metal interconnection structure is fabricated in reduced steps.
The present invention provides a novel metal interconnection structure for evaluation on electromigration thereof, wherein a test metal interconnection to be evaluated on electromigration is connected through a plurality of bamboo-structured metal interconnections to a plug metal interconnection, and the bamboo-structured metal interconnection has a smaller sectioned area than the test metal interconnection whilst the plug metal interconnection has a larger sectioned area than the test metal interconnection.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.